This invention relates to a consumable electrode remelting furnace, such as a vacuum arc remelting (VAR) furnace or an electroslag remelting (ESR) furnace, in which changes in the weight of the consumable electrode are monitored as the electrode is remelted. This invention particularly relates to such an improved furnace and a method of operating the same which lend themselves to more accurate control of melting rates during the remelting process.
In a consumable electrode remelting furnace, it is highly desirable to be able to monitor the decrease in the consumable electrode's weight as it is remelted in the furnace mold. This permits the remelting process to be closely watched as its end approaches, so that the process can be halted when as much as possible of the metal in the electrode has been remelted into an ingot but before the electrode holder or clamp at the top of the electrode has been exposed to the electric arc generated at the bottom of the electrode. It is also greatly desired to monitor the weight of the electrode, so that the melting current can be varied during the remelting process with reductions in the weight of the electrode so as to control: (1) the volume of the molten metal pool on the ingot being formed in the furnace mold; and (2) the metallurgical properties of the ingot.
However, such furnaces and methods of operating the same have left much to be desired in that they have failed to provide the desired degree of accuracy and reproducibility in monitoring the weight of consumable electrodes and have generally required systems that are relatively complicated and expensive to install and maintain in the furnaces. In this regard, it has been found to be particularly difficult to monitor the weight of an electrode in a VAR furnace. For example, in Wynne U.S. Pat. No. 3,379,818, granted Apr. 23, 1968, and Wooding U.S. Pat. No. 3,272,905, granted Sept. 13, 1966, one or more load cells for monitoring electrode weight have had to be mounted within a special protective hollow housing connecting the electrode ram and the electrode clamp in a VAR furnace. Besides the inherent difficulty and expense of installing and maintaining load cells in the required special housings, such arrangements have inevitably suffered adverse effects from electrical interference with the load cells' electrical output due to the load cells close physical proximity to the path of the extremely high electrical currents required to melt the electrodes. In Scheidig et al U.S. Pat. No. 3,614,284, granted Oct. 19, 1971, load cells for monitoring electrode weight have had to be positioned atop a VAR furnace under a special weighing platform which bears, besides the weight of the electrode, electrode ram and electrode clamp, the added weight of the motor and transmission that move the electrode, as well as the added weight of a current carrying cable (e.g., a total added weight estimated to be about 500 to 1,000 pounds for a furnace to remelt an electrode of up to about 10,000 pounds). Such added weight of the motor, transmission and cable has required the use of load cells with heavier weighing capacities, i.e., greater weight range, and less accuracy than load cells that could be used if such added weight were not borne by the load cells.
There has been a need, therefore, for simpler and more accurate ways of monitoring the weight of an electrode in a consumable electrode remelting furnace.